Of the thousands of cases Sonia Sotomayor has heard during nearly 17 years on the federal bench, the one likely to raise the toughest questions during her Supreme Court confirmation hearings, which begin on July 13, involves affirmative action. In 2007 Sotomayor, as a member of the Second Circuit Court of Appeals, heard arguments in the case of Ricci v. DeStefano. In that case, white firefighters in New Haven, Conn., challenged the city's decision to ignore the results of a promotion test after there were no black firefighters among the top scorers. One of 20 white firefighters who brought the case,...